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Fertilizers, Pest Control and Soil Management
Organic Gardening
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Soil Amendments and Mulches

What's a soil amendment? What's a mulch? Which do you need, and why? "Mulch" is a generic term used to describe any material, organic or inorganic, placed on the ground around plants. Mulches can serve a number of purposes, but their primary use is to control weeds and moisture. A soil amendment is something you mix into the soil to improve its texture and/or its nutrient- and water-holding ability. Some materials can be used as either; some are better suited for one purpose.

The most commonly used organic mulches are wood-based. Typically, they are comprised of shredded bark (in this area, a mixture of hemlock and fir) run through a shredder to a graded size. The two most common grades are extra fine (the consistency of sawdust) and medium fine, which is generally comprised of pieces which can pass through a 2-3" screen.

Another common wood-based mulch is composed of sawdust or shavings mixed with high-nitrogen organic matter and then composted. Sky only carries varieties that use cow, chicken, and horse manure as the nitrogen sources, not sludge. Fertil-Mulch® is the finer-textured mulch of this sort, Chicken N' Chips® the coarser. Neither will burn plants, and both will add small amounts of plant nutrients as they work their way into the soil.

Less commonly used wood-based mulches are play chips (cedar wood chips) or ground tree waste from arborists (usually mixed wood chips, bark, and needles). Remember that the more uncomposted the wood/bark in your mulch, the greater the chance that it will compete for available nitrogen in your soil as it breaks down. To compensate for this, it's best to broadcast under your mulch a balanced fertilizer such as Dr. Earth All Purpose.

Finally, compost of any kind and more exotic materials such as cocoa beans or hazelnut shells may all be used as mulches. Compost is great for retaining moisture.

For soil amendments, the ideal product to use is compost. Sky carries, in bulk or bags, Cedar Grove Compost, which is a screened organic material made from composted green waste and food waste from the urban recycling program. No chemicals or sludge by-products are added. It contains nitrogen, phosphorus, potassium, and a wide range of micronutrients. Inert particles and pieces are commonly found in the green waste; some level of inert material may still be present after the product is cleaned and processed. These materials will not harm your plants, vegetables, or landscape.

Chicken N' Chips® and Fertil-Mulch® are recommended for incorporating into the soil for ornamental plantings and are especially good for improving heavy clay soils. Finally, Sky carries an assortment of excellent bagged composts for use as soil amendments: Gardner & Bloome Soil Building Compost™ and Harvest Supreme™, E.B. Stone Planting Compost, mushroom compost, composted steer and chicken manure, and more.

Still not quite sure which to use? Tell us what your soil is like and what you're planting, and we can help!

By Terri Williamson
Skylights Spring/Summer 2009, Vol 24, No. 2

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Sky Nursery
18528 Aurora Avenue North
Shoreline, WA 98133
(206) 546-4851

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